The objective of this research will be to elucidate the mechanism of Ca plus 2-release from the sarcoplasmic reticulum. This project will use an improved prepration (skinned skeletal muscle fibers of the frog). These skinned fibers will be mounted in a tension transducer, immersed in solutions of different ionic composition, and at appropriate times lifted from these solutions and longitudinally electrically stimulated. During all solution changes and electrical stimulation the tension developed by the fiber will be measured. The effects of electrical parameter of longitudinal electrical stimulation on tension development will be determined. Sudden changes in the ionic composition of the solution bathing the fiber will be made to determine the effect that depolarization and repolarization of the sarcoplasmic reticulum have on Ca plus 2 release. The effects that certain chemical stimuli (sudden increases in Ca plus 2 concentration, caffeine, and sudden decreases in Mg plus 2 concentration) have on Ca plus 2 release from the sarcoplasmic reticulum will be investigated and their interacton with chemical changes in the bathing solutions which cause repolarization and depolarization of the SR will also be evaluated. The interaction of the electrical parameters and chemical condition that cause Ca plus 2 release will be determined. All of these results will then be analyzed to determine the relative importance of the hypothesized mechanisms of Ca plus 2 release from the SR (e.g., Ca plus 2 induced release or depolarization induced release from the SR).